Effects of viscosity on turbine mode performance and flow of a low specific speed centrifugal pump

The performance and flow of a low specific speed experimental centrifugal pump as turbine are identified by means of CFD method when it handles a more viscous liquid than water. The performance curves are compared among five kinds of liquids. Meanwhile the internal variables, such as impeller theoretical head, total hydraulic loss coefficients across the machine, individual total loss coefficient in suction pipe/draft tube, impeller and volute, averaged skin friction factors, pressures coefficients over blade surfaces as well as incidence loss are explored. The correction factors of flow rate, head, hydraulic efficiency and impeller theoretical head in both turbine and pump modes are correlated to impeller Reynolds number by a three-parameter-power function. The flow behaviours in turbine mode are characterized by examining the velocity magnitude and flow angle at the volute outlet, angle of attack, fluid velocity vectors in the volute, swirling patterns of flow in the draft tube and deviation angle at impeller outlet. The results can be useful for pump model selection, performance prediction, hydraulic design and impeller geometry modification.